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Demonstration of several problematic cases. Light bleeding is shown in (a), where a strong light source is directed at the far side of a thin object. The near side, visible by the camera, is affected by light bleeding through the object. When the camera is placed on the other side of the same object (b), the problem with extreme initial distributions of radiance becomes visible. In (c), a single propagation iteration is taken.
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This paper introduces a new GPU-based, real-time method for rendering volumetric lighting effects produced by scattering in a participating medium. The method includes support for indirect illumination by scattered light, high-quality single-scattered volumetric shadows, and approximate multiple scattered volumetric lighting effects in isotropic an...
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... former is mainly visible in scenes with many thin separating features (e.g., thin walls) that cut through voxels. Figure 6a demonstrates this effect. Light bleeding is men- tioned by Kaplanyan and Dachsbacher [2010], who suggest that their cascaded LPV approach reduces bleeding to some degree. ...
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... initial distributions are some- what tricky to deal with, as they break the assumption that the LPVs are used to simulate low-frequency effects. Figure 6b demonstrates the problem by aiming a strong light source at a small surface area (the surface area is completely contained within a voxel). ...
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... the number of propagation iterations can also reduce blockiness at the cost of performance, although large fuzzy block- ing may interfere with the smoothing from extra propagation. In Figure 6c we perform only one propagation iteration to illustrate the problem. With the suggested eight propagation iterations we do not observe this problem in the absence of large fuzzy blocking. ...
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Citations
... We exclude some materials in which single scattering can influence appearances significantly, such as low-concentration liquid, lowdensity cloud and fog [NGD*06, KF12,SZLG10]. • Observer outside: Some participating media problems consider a global effect, meaning the medium involves the entire scene, including the viewpoint or camera [SDS*16, BSA12]. In contrast, BSSRDF approaches aim only to estimate the radiance leaving the translucent object and are limited to objects that the observer cannot enter. ...
Sub‐surface scattering is always an important feature in translucent material rendering. When light travels through optically thick media, its transport within the medium can be approximated using diffusion theory, and is appropriately described by the bidirectional scattering‐surface reflectance distribution function (BSSRDF). BSSRDF methods rely on assumptions about object geometry and light distribution in the medium, which limits their applicability to general participating media problems. However, despite the high computational cost of path tracing, BSSRDF methods are often favoured due to their suitability for real‐time applications. We review these methods and discuss the most recent breakthroughs in this field. We begin by summarizing various BSSRDF models and then implement most of them in a 2D searchlight problem to demonstrate their differences. We focus on acceleration methods using BSSRDF, which we categorize into two primary groups: pre‐computation and texture methods. Then we go through some related topics, including applications and advanced areas where BSSRDF is used, as well as problems that are sometimes important yet are ignored in sub‐surface scattering estimation. In the end of this survey, we point out remaining constraints and challenges, which may motivate future work to facilitate sub‐surface scattering.
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In this paper, we present an enhanced subsurface light propagation volumes (ESLPV) method for real-time rendering of translucent materials. Our method is an extension of the subsurface light propagation volumes (SSLPV) (Proceedings of the ACM SIGGRAPH Symposium on High Performance Graphics, HPG ’11, pp 7–14 ACM 2011) technique. We improve the SSLPV by incorporating a single-scattering framework that uses the same spherical harmonics (SH) storage structure as the SSLPV. The new single-scattering technique deposits radiance as SH coefficients during a ray marching procedure. The final result is rendered using a ray tracer with importance sampling along the camera ray. This framework also enables the ESLPV to render refractive objects. In addition, we also propose a distance transform optimization that can remove the unnecessary computations during the propagation cycle of LPV (Proceedings of the 2010 ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, I3D ’10, pp 99–107 ACM 2010) based methods. A hierarchical propagation process is also proposed to render highly translucent materials. Similar to the SSLPV, our ESLPV method contains no precomputations, and has low storage requirements that are independent of the mesh size.
Efficient light transport simulation in participating media is challenging in general, but especially if the medium is heterogeneous and exhibits significant multiple anisotropic scattering. We present Principal-Ordinates Propagation, a novel finite-element method that achieves real-time rendering speeds on modern GPUs without imposing any significant restrictions on the rendered participated medium. We achieve this by dynamically decomposing all illumination into directional and point light sources, and propagating the light from these virtual sources in independent discrete propagation domains. These are individually aligned with approximate principal directions of light propagation from the respective light sources. Such decomposition allows us to use a very simple and computationally efficient unimodal basis for representing the propagated radiance, instead of using a general basis such as spherical harmonics. The resulting approach is biased but physically plausible, and largely reduces the rendering artifacts inherent to existing finite-element methods. At the same time it allows for virtually arbitrary scattering anisotropy, albedo, and other properties of the simulated medium, without requiring any precomputation.
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